When loading or unloading a vehicle (e.g., a truck, trailer, etc.) parked at a loading dock, it is generally a safe practice to help restrain the vehicle from accidentally moving too far away from the dock. This is often accomplished by a hook-style vehicle restraint that engages what is often referred to in the industry as a vehicle's ICC bar (Interstate Commerce Commission bar) or RIG (Rear Impact Guard). An ICC bar or RIG comprises a bar or beam that extends horizontally across the rear of a vehicle, below the bed of the truck or trailer. Its primary purpose is to help prevent an automobile from under-riding the vehicle in a rear-end collision. A RIG, however, also provides a convenient structure for a hook-style restraint to reach up in front of the bar to obstruct the bar's movement away from the dock.
To release the vehicle and prepare for the next one to enter, the restraint retracts to a lowered position free of the bar. Sometimes, however, forward pressure from the vehicle causes the restraint's hook to catch on the bar in a way that prevents the hook from retracting. Such a condition, if recognized by the driver of the vehicle, is readily remedied by what is known as a “bump-back,” where the vehicle momentarily backs up slightly to release the pressure and thus allow the hook to retract.